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intersectionLite

Returns elements from the source array that also exist in the target array. Lightweight version of the intersection function optimized for small arrays (< 100 elements). Uses indexOf for element checking instead of Set, providing better performance for small arrays while maintaining O(n*m) complexity.

Signature​

const intersectionLite: <Type>(source: Type[], target: Type[]) => Type[]

Parameters​

NameTypeDescription
source-Source array to use as base for intersection
target-Target array to compare against

Returns​

Array of elements that exist in both arrays

Examples​

Basic intersection of number arrays​

import { intersectionLite } from '@winglet/common-utils';

const array1 = [1, 2, 3, 4, 5];
const array2 = [3, 4, 5, 6, 7];

console.log(intersectionLite(array1, array2)); // [3, 4, 5]

String array intersection​

const fruits1 = ['apple', 'banana', 'orange', 'grape'];
const fruits2 = ['banana', 'grape', 'kiwi', 'mango'];

console.log(intersectionLite(fruits1, fruits2)); // ['banana', 'grape']

Finding common user IDs​

const activeUserIds = [1, 2, 3, 4, 5, 6];
const premiumUserIds = [3, 4, 5, 7, 8, 9];

const activePremiumUsers = intersectionLite(activeUserIds, premiumUserIds);
console.log(activePremiumUsers); // [3, 4, 5]

Working with duplicates​

const source = [1, 2, 2, 3, 4, 4, 5];
const target = [2, 4, 6];

console.log(intersectionLite(source, target)); // [2, 2, 4, 4]
// Note: Duplicates from source are preserved if they exist in target

Case-sensitive string matching​

const words1 = ['Hello', 'World', 'hello', 'world'];
const words2 = ['Hello', 'world', 'Test'];

console.log(intersectionLite(words1, words2)); // ['Hello', 'world']
// Case-sensitive: 'hello' and 'World' don't match

Finding common elements between datasets​

const currentUsers = ['alice', 'bob', 'charlie', 'diana'];
const invitedUsers = ['bob', 'charlie', 'eve', 'frank'];

const alreadyRegistered = intersectionLite(currentUsers, invitedUsers);
console.log(alreadyRegistered); // ['bob', 'charlie']
console.log(`${alreadyRegistered.length} invited users are already registered`);

Edge cases​

// Empty arrays
console.log(intersectionLite([], [1, 2, 3])); // []
console.log(intersectionLite([1, 2, 3], [])); // []
console.log(intersectionLite([], [])); // []

// No common elements
console.log(intersectionLite([1, 2, 3], [4, 5, 6])); // []

// All elements in common
console.log(intersectionLite([1, 2, 3], [1, 2, 3])); // [1, 2, 3]

Working with mixed data types​

const mixed1 = [1, '2', 3, '4', 5];
const mixed2 = ['2', 3, '4', 6];

console.log(intersectionLite(mixed1, mixed2)); // ['2', 3, '4']
// Note: Uses strict equality (===) for comparison

Permission intersection​

const userPermissions = ['read', 'write', 'delete', 'admin'];
const requiredPermissions = ['read', 'write', 'execute'];

const grantedPermissions = intersectionLite(userPermissions, requiredPermissions);
console.log(`User has ${grantedPermissions.length} of ${requiredPermissions.length} required permissions`);
console.log('Granted:', grantedPermissions); // ['read', 'write']

Playground​

import { intersectionLite } from '@winglet/common-utils';

const array1 = [1, 2, 3, 4, 5];
const array2 = [3, 4, 5, 6, 7];

console.log(intersectionLite(array1, array2)); // [3, 4, 5]

Notes​

Performance Optimization: This is a lightweight alternative to the standard intersection function.

  • For arrays with < 100 elements: Uses indexOf (O(n*m)) which is faster due to lower overhead
  • For arrays with >= 100 elements: Consider using intersection which uses Set (O(n+m))
  • Optimized loop structure with cached element reference reduces array access overhead

When to Use:

  • Small arrays (typically < 100 elements)
  • Performance-critical hot paths with small data sets
  • When Set construction overhead outweighs O(n*m) complexity

Equality: Uses JavaScript's strict equality (===) via indexOf. This means NaN !== NaN (unlike Set.has() which uses SameValueZero).

Order Preservation: Maintains the original order of elements from the source array in the result array. Elements appear in the result in the same order they appear in source.

Duplicate Handling: If the source array contains duplicates and those elements exist in the target array, all occurrences from the source will be included in the result.

Memory Efficiency: Uses direct array indexing and avoids Set construction overhead. Result array grows dynamically without pre-allocation.